Watch cases are already known in the prior art in which the crystal is directly fixed to the caseband. It has thus been proposed in the European published patent specification EP No. 0 066 538 to fasten a watch crystal by soldering, particularly one formed of a monocrystalline hard material such as sapphire, the periphery of such crystal being dimensioned to correspond to that of the caseband in a manner such that neither bezel nor fastening snap of the crystal to the caseband is necessary. According to this document, metallization layers cover a portion of the internal surface of the crystal in order to hide the solder and to assure its adhesion to the crystal. This method of fastening the crystal gives the case a novel and very elegant aesthetic to the extent that the caseband (or bezel) no longer surrounds the crystal. Since the crystal is preferably realized in a hard material such as sapphire, the most exposed parts of the case are thereby protected against scratch damage which might eventually occur.
It has long been known that the elegance of the watch is in large measure a function of its thickness, extra thin watches being generally those at the top of the quality range. In addition to their elegance, very thin watches are likewise more agreeable to wear to the extent that they are better integrated to the arm. The impression of thickness of a watch is not an entirely objective criterion, it being known that it is not solely a function of a measurable dimension at the center thereof, but also of the general form, i.e. the impression of thickness being largely conditioned by the height of the side face of the caseband. In fact, at the time of purchase of a watch, as far as the thickness is concerned, the criterion which counts for the most is not the measurable thickness, but the impression of thickness which the buyer perceives, and particularly the impression of thickness which the watch gives when worn. With this end in view, many cases exhibit a back cover extending below the level of the caseband in order to reduce the height of the side face of this latter. At the same time, if this artifice is exaggerated, it has as an effect to distance the caseband from the wrist when the watch is worn, being given that the surface of the wrist on which the back cover of the watch rests is slightly outwardly curved. This does not lead however to a better integration of the watch with the arm.
The purpose of this invention is thus to provide a solution which enables giving a watch case the impression of being apparently thinner than its real thickness, particularly when worn, and at the same time giving it more solidity and rendering it less vulnerable to the attacks to which it is daily subjected on the arm of the wearer.
In order to attain this purpose, the crystal has the form of an essentially spherical cap, of which at least a part of the periphery is situated at a level lower than that of the dial.
Publications are certainly known describing a watch case in which the crystal comprises a spherical surface or at least an outwardly curved surface, the periphery of which is at least partially at a level below that of the dial. Such may be found in particular in the French utility certificate FR No. 2 077 642 and French patent FR No. 1 398 410. In the watch cases which are described therein, the crystal is of an organic material and could only with difficulty be otherwise owing to the fact that the periphery thereof must be formed in order to obtain and assure the fastening of the crystal to the caseband. This necessitates moreover an extra thickness of the periphery in order to assure a good retention thereof.
It follows that the crystal is manufactured from an easily scratchable material. Moreover, the bevelling is limited.
In contrast thereto, the watch case according to the invention may present a side surface of the caseband reduced to a height just sufficient to prevent it from presenting a cutting edge. Thereby, with the crystal preferably formed of hard monocrystalline material, almost the only part of the case susceptible to shocks and scratches is realized from an unscratchable material. Moreover, thanks to its spherical cap form, the crystal enables better absorption of the shocks to which it may be subjected by transmission thereof to its seat situated on the caseband to which it is fastened (operation of a vault effect). Thus, in addition to the aesthetic effect which the solution presented by the invention confers to the watch case, it offers an excellent protection from shocks and pressures to which the watch is exposed. While extra thin watches have generally been de luxe watches of a relatively fragile nature, the solution proposed herein enables the combining of strength with great elegance. It is thus that such a watch having high resistance to pressure and external attacks may be worn without fear of deterioration in all circumstances of modern life and even in conditions as severe as may be encountered in subacquatic diving, even although it has not been especially conceived to this purpose.
A further advantage to take into consideration, deriving from the spherical cap form of the crystal, resides in the manner of manufacture thereof when it is of monocrystalline mineral material which, as is well known, may not simply be moulded as plastic watch glasses but on the contrary must be cut. A sample geometric form such as the spherical cap is easier to realize than known outwardly curved crystals having various radii of curvature, of the type intended to be fixed by a bezel or caseband snap for instance.